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January 3, 2025 HWA Project No. 2021-159-21 Geotechnical Engineering Report 31 HWA GEOSCIENCES INC. Port Gardner Storage Facility 5Pile diameter corresponds to pile type (e.g., piles shall be 8-inch-diameter micropiles or 18-inch-diameter concrete-filled driven piles). Provided the piles have a center-to-center spacing of at least 3D, where D is the diameter of the piles, the pile group capacity can be taken as the sum of the individual pile capacities. If the center-to-center pile spacing is less than 3D, the individual capacities should be reduced accordingly. 4.6.2 Down Drag Loading on Vertical Piles Down drag loading occurs when soil settlement relative to pile settlement is sufficient to mobilize side friction in the downward direction (negative side resistance). Small relative downward movements between the soil and the pile on the order of ¼ inch are sufficient to fully mobilize negative shaft resistance or down drag. Hence, down drag loading must be considered in design of the pile foundations due to the anticipated liquefaction-induced settlement. Factors that directly contribute to the magnitude of the down drag loads experienced by each deep foundation element include the elevation of the pile cap, thickness of the liquefiable soil layer, the skin roughness based on pile type, and the pile diameter. HWA assumed residual shear strengths of the liquified soil layer when considering down drag loading. A summary of down drag loading for all proposed pile-supported areas and respective structures is presented in Table 3. Table 3. Down Drag Loading – Proposed Pile-Supported Areas Area - Structure Pile Cap Elevation (feet)1 Tip Elevation (feet)1 Pile Length (feet) Pile Diameter (inches)3 Down Drag Loading (kips)4 Seismic Area 10 – CS Vault 10-01 8 -25 33 8 15 Area 15 – CS Manhole 15- 01 -3 -50 47 8 20 Area 15 – CS Manhole 20- 01 -2 -22 20 8 5 Area 20 – CS Debris Removal 4 -20 24 8 5